(57) @ A disinfectant or antiseptic composition containing al- kyldimethylbenylammonium or a salt thereof in which a content of dodecyldimethylbenzylammonium or a salt thereof is at least about 80% by weight exhibits its germicidal activity widely against a broad spectrum of microorganisms in a short period with organic materials, as compared with the conventional benzalkonium chloride compositions. Further, when the above disinfectant or antiseptic composition is used in combination with one or more members selected from the group consisting of lower alcohols, chelating agents and amphoteric or nonionic surfactants, more significant bactericidal and disinfecting effect can be _I produced.